初始化 Pair 的向量<int,int>带有 emplace_back</int,int>

Question

I want to initialize a vector of integer pairs while specifying its size (I have to use this structure). I tried:

vector<pair<int, int>> container;
container.emplace_back(size);

And:

container.emplace_back(size, make_pair(0, 0));

But I keep having this error:

error: no matching function for call to 'std::pair<int, int>::pair(long long unsigned int&, std::pair<int, int>)'

Is there any solution or different approach?

Thank you!

Answer 1

emplace_back forwards its parameters to the elements constructor. std::pair<int,int> has no constructor that takes a size and a pair, hence the error. To emplace an element:

std::vector<std::pair<int, int>> container;
container.emplace_back(0,0);

However, if you want to construct a vector of certain size upfront, you need not emplace elements, because they are already there:

std::vector<std::pair<int, int>> container(size);
container[42] = make_pair(1,2);   // 42 < size   !

Answer 2

I'm guessing what you really want is something like:

vector<pair<int, int>> container(size);

This will initialize the vector constainer with size number of default-constructed elements.